I've never had to do it. Bicycles don't vibrate and there are no hidden or hard-to-reach bolts.
??? Your tyres must be very soft or you ride on extra smooth tarmac, I have had to use Loctite on rack mountings, mudguards, etc ...
Washers, certainly plain and spring washers, actually increase the chances of a screw untightening.
Loctite comes in various different strengths, of course. 222 is probably the most appropriate stuff for bikes. 243 is a bit strong, and 272 is as good as welding the thing up, so not recommended.
I've since noticed blue stuff on some bolts on my new bikes. I'm assuming this is threadlock.
Guess I'll just see what works loose and threadlock them.
Martin